Brief:
I designed this odd, little 5-tube tubefin with one purpose in mind: as an ultra low-cost, me bucko, quick-buildin' L1 certification for 14 year old rocketeers under t' new NARRRRR junior cert program. After spendin' so much effort figuring out how t' make tubefin rockets more efficient, ya bilge rat, I "retro-engineered" this one (I think that's t' right term) to have very high drag, t' better t' use H-power in a small, inexpensive rocket. Aye aye! Blimey! I call it "ElCheapoCerto", but it is basically a double size version (2.33x scale, ya bilge rat, actually) o' t' neat new 5-tube tubefin "TOOBOH" now avaiiable from Discount Rocketry.

Construction:
ElCheapoCerto ("ECC") is constructed from 38mm motor tube with 2" postal mailin' tubin' for t' tube fins. Avast, me proud beauty! Parts count is seven (body tube, tube fins, ya bilge rat, matey, nose cone). Arrr! There is no internal structure and it flies on 38mm motors or 29mm motors usin' a standard adapter. Aye aye! Blimey! It can be scratch built in an hour for about 20 bucks includin' cutting out parts and painting. Ya scallywag! T' parts list:

• 38mm LOC nose cone
• 3" piece o' LOC motor tube
• 5 x 3" tube fins cut from 2" heavy mailin' tube (white-paper faced)
• Also required: a 1" fiber 1/4" launch lug, a 24" Top-Flite nylon chute (use 28"-30" size to assure descent below 6m/s per L1 cert rules and Safety Code), matey, 8' o' quality para cord, matey, and 5 popsicle sticks. Avast! For 29mm motors, I used a LOC 29-38mm adapter kit. Well, blow me down! Avast, ya bilge rat, me proud beauty! 5-minute epoxy was used throughout. Begad! Well, blow me down!

Assembly sequence:

1. Cut t' popsicle sticks in half and glue halves together t' make four double thick, me bucko, me bucko, me hearties, leavin' t' rest single thick halves.
2. Cut up t' 2" x 24" mailin' tube into 3" sections for t' tube fins. Avast, me proud beauty! Use a razor saw or a very fine hack saw t' do this.
3. Seal t' cut surfaces o' t' tube fins with a strip o' 3/4" maskin' tape, me hearties, top and bottom. If you partially snip it at intervals, matey, me bucko, me bucko, it won't bunch on t' inside o' t' tube.
4. Glue t' doubled Popsicle stick halves t' four o' t' 5 tube fins, me hearties, leavin' one plain. Well, blow me down! Avast! These will be t' spacers between t' tube fins.
5. Workin' on a large flat surface, ya bilge rat, which had better not be t' good dinin' room table, arrr, t' assure perfect alignment, glue t' plain (not popsicle stick) tube fin t' t' body tube 1.25 inches up from t' bottom. Begad! Don't skimp on the epoxy.
6. When dry/hard, glue one o' t' tube fins with t' Popsicle stick spacer next t' t' first, havin' t' point of contact with t' neighbor bein' t' spacer stick, ya bilge rat, which should fit flat/flush. Begad! Arrr! Use plenty o' epoxy but don't slop it into t' triangular space betwixt tube fins and t' body.
7. Repeat this process until you get t' t' last one. Ahoy! There will remain a gap o' as much as 1/4" betwixt the last and t' first tube fins. Just fill it in with half-Popsicle stick spacers (I needed 3 o' them). Avast, me proud beauty! T' slight asymmetry won't be noticed by t' rocket or anybody else.
8. T' 1/4" launch lug is glued in place 5" above t' tube fin can and exactly inline with one o' the triangular spaces betwixt tube fins which you remembered nay t' slop glue into. Blimey! Avast! T' 1/4" launch rod passes through here.
9. T' shock cord is installed by drillin' a 1/8" hole into t' body tube 6" from t' top and on the opposite side from where t' launch lug is. Avast, me proud beauty! Pass para cord through t' hole and use a knot as a stop. Begad! Ya scallywag! T' knot is covered by a reasonably streamlined piece o' plastic cut from a plastic cigar tube or from a split Sharpie pen cap or the like, shiver me timbers, usin' plenty o' epoxy t' anchor it.
10. You are now done. I finished mine with rattle-can spray paint. Arrr! Instead o' usin' a manly color like red, me bucko, me hearties, arrr, orange, camo or blue, I chose a pleasant shade o' lavender-lilac I had layin' around (and as Jerry Seinfeld would say, "And thar's nay a thin' wrong with that!"). Begad!
11. Parachute is attached t' t' shock cord and t' LOC cone in t' usual way (i.e., by drillin' me own holes instead of usin' t' fragile hoop on t' base).

Flight:
To date, I have rarely found it necessary t' add nose ballast with any tube fin design. Aye aye! Well, blow me down! But t' insure safety with the 310 gram H73 motor and casin' on a rocket weighin' only 425 grams, I did put 50 grams o' copper BBs into t' nose cone. Plus, matey, it lowers t' maximum speed by about 10% or so, and I try nay t' fly non-glassed tube fins at more than 500 mph. This is nay needed with F and G motors. Blimey! Blimey! First flight be on an AeroTech F42-4 usin' a 29-38 adapter and was perfect and vertical despite a 10-12 mph breeze. Ahoy! It went t' about 600-700'. For all later flights, I taped an 18mm parasite pod with PerfectFlite altimeter t' t' side so I could calculate Cd from t' altitude achieved (this increases the effective diameter from 42mm t' 46mm but otherwise doesn't affect flight dynamics. Aye aye! Next flight on an H73-10 went to 1981', givin' calculated Cd=1.90 at 295 mph, which was about what I expected based on 6-tube tube fins. Avast! Next flight on an elderly G38-7 I had in me box was a disaster--the EconoJet CATO'd like a cherry bomb, shatterin' t' LOC adapter into pieces and splittin' open t' aft 12" o' t' rocket betwixt two o' t' tube fins. Arrr! Avast! I decided I could salvage the thin' by just permanently gluin' a new 29-38mm adapter into ECC. Arrr! T' idea worked great but meant that all future flights would have t' be 29mm motors. Nay a problem. Blimey! Ahoy! Next came two perfect flights on H97J-10 motors with average height o' 1992' and Cd=1.74 at 444mph. I think this is probably t' preferred motor for L1 in this design, along with the 38mm H73J-10 as a second choice (slower climb and less wind resistance). Aye aye! No other H-motors are recommended although I did (on a dare) make one successful flight on an H180-10, which t' Perfectflite recorded as 2136' and Cd=1.76 at 509 mph (faster than is prudent unless t' tube fins are glassed). That said, me bucko, I blew a tube fin off ECC both times I tried flyin' it on H128-10 motors. Aye aye! Nay good. Blimey! So H power in ECC should be limited t' t' H73 and H97 Blackjack motors. The minimum Cd value obtained in flight testin' o' ECC is about 1.75, which compares reasonably with t' calculated value of minimum Cd = 1.63, based on its dimensions above t' tube fin can and t' regression equation for 6-tube tube fins. So 5-tube tube fins and t' usual 6-tube tube fins perform similarly. Arrr! Huge Drag Coefficients are needed here t' avoid overspeedin' t' airframe o' this small, light rocket. Avast, me proud beauty! Begad! Flight testin' o' ECC with additional F-G motors gave even higher Cd values at speeds o' 200 mph and lower as expected--about 2.30 t' 2.80. Details o' these test flights:

• F23-4 682' at 159 mph
• F27-4R 589' at 150 mph
• F50-6 868' at 224 mph
• G40-7 1314 at 237 mph

Summary:
I would say t' goal o' a unique, simple, and cheap L1 certification rocket for 14 and above rocketeers seekin' to certify under t' new NARRRRR rules has been achieved. Well, blow me down! Blimey! For fun flying, it will go t' 1300' or more on G-power, which is as high as you want t' fly at our island launch site anyway. Ya scallywag! Blimey! Ahoy! Blimey!

CONs: Hard t' see at 2000'. Limited H power choices (H73J-10 or H97-10). Aye aye! Tube fins can be dented by handin' on hard surface.